As used herein, the term "fiber" includes fibers of extreme or indefinite length ("filaments") and fibers of short length ("staple"). The term "fabric" denotes a two, or possibly three, dimensional product built up from fibers. These fibers may occur in the fabric uni-directionally, bi-directionally with different warp and woof ratios or tri-directionally. The terms "mixed fiber" or "mixed fibers" refer to yarns composed of two or more different types of fibers. The terms "multicomponent fiber" or "multicomponent fibers" refer to fibers having two or more longitudinally coextensive components. The terms "multicomponent yarn" or "multicomponent yarns" refer to either mixed fiber yarns, multicomponent fibers, or mixtures of them.
Fiber reinforced products are known. Such products make possible the manufacture of advanced thermoplastic composite parts in very complex shapes. The traditional composites take the form of a thermoplastic matrix reinforced by non-thermoplastic fibers, such as graphite, glass, ceramics and similar fibers. These materials may be found in many "high-tech" applications such as for aircraft components and recreational equipment.
U.S. Pat. No. 4,539,249 ("'249") describes laminates of graphite, glass, aramides, ceramics, quartz, boron, SiC, etc., and resinous thermoplastic fibers which are intended for conversion into a composite. To make the pre-consolation form, resinous thermoplastic fibers are combined or blended with the reinforcing fibers to form a single yarn. The blended yarn is then woven into a fabric that is shaped to a suitable form in a mold and then heated to melt the thermoplastic component. Also described is a process for spinning staple resin fibers with graphite to form the yarn which is then woven into the fabric, shaped and heated. Fabrics formed by interweaving the graphite in the resin fibers by conventional weaving techniques is also disclosed.
U.S. Pat. Nos. 4,874,563 ("'563"), 4,818,318 ("'318"), and 4,871,491 ("'491") describe methods of forming fiber reinforced composites by forming a tape or fabric prepreg especially of carbon fiber tows intermixed with thermoplastic matrix fibers. Also described is a process involving the extrusion of carbon fiber tapes impregnated with high melting thermoplastic polymers. These patents acknowledge that prepregs formed by forming composites from carbon fibers which are coated or painted with thermosetting matrix materials are stiff and can not be draped across intricately shaped molds or are tacky and difficult to handle. The patents disclose attempts to overcome the shortcomings of such former processes by intermixing tows of carbon fibers and thermoplastic polymeric fibers. The processes for such intermixing are disclosed. '318 discloses intermixing two tows where one tow is a thermoplastic matrix material and the other tow is a reinforcing material that is preferably carbon fiber but may be a sufficiently high melting thermoplastic. '491 and '563 also describe an intermixing method.
U.S. Pat. Nos. 5,000,807 ("'807") and 5,177,840 ("'840") both disclose additional methods of commingling or combining thermoplastic matrix and, preferably, non-thermoplastic reinforcing fibers. The reinforcing fibers may be aromatic polyamides.
Cziollek, J., "New Yarns for Thermoplastic Technical Textiles and Composites", Technische Textilien/Technical Textiles, Vol. 35, October 1992, pp. E106-E107 describes attempts to develop a 100% thermoplastic composite material in which both the reinforcing fiber and the matrix polymer are thermoplastics. This article describes theoretical methods of making such a composite yarn but does not sufficiently describe the matrix polymer or any specific combination of thermoplastic reinforcing fiber with a matrix polymer. The discussion is primarily directed to development of a reinforcing fiber and is not enabling for a complete composite fabric.
U.S. Pat. No. 5,190,809 ("'809") discloses a fabric of continuous thermoplastic matrix filaments and continuous reinforcing filaments suited for being processed as a thermoplastic composite prepreg. In one variation of the fabric, both the reinforcing filament and the matrix filament are thermoplastics. Even in the case where both the reinforcing and matrix filaments are thermoplastic, '809 teaches that each type of filament is supplied as a discrete bundle or monofilament.
A problem inherent in combining two or more thermoplastic materials is the incompatibility of the separate materials. For reinforced composite applications, it is essential that the matrix polymer completely coat or "wet out" the reinforcing fiber. Air pockets that remain in the final product seriously reduce its strength. One manner of easing the problem of insufficient wet out is by adding a size, i.e., a wetting agent or water soluble polymer, to the matrix polymer to improve the wet out of the reinforcing polymer.
U.S. Pat. No. 5,187,018 discloses the use of a compatibilizer to promote wetting of the reinforcing fiber by the matrix thermoplastic. The reinforcing fiber and the compatibilizer may be co-extruded.